2-methylbutyryl-CoA dehydrogenase deficiency associated with autism and mental retardation: a case report

Biomarkers of mitochondrial dysfunction in autism spectrum disorder: A systematic review and meta-analysis

Autism spectrum disorder (ASD) is a neurodevelopmental disorder affecting 1 in 36 children and is associated with physiological abnormalities, most notably mitochondrial dysfunction, at least in a subset of individuals. This systematic review and meta-analysis discovered 204 relevant articles which evaluated biomarkers of mitochondrial dysfunction in ASD individuals. Significant elevations (all p < 0.01) in the prevalence of lactate (17%), pyruvate (41%), alanine (15%) and creatine kinase (9%) were found in ASD. Individuals with ASD had significant differences (all p < 0.01) with moderate to large effect sizes (Cohen's d' ≥ 0.6) compared to controls in mean pyruvate, lactate-to-pyruvate ratio, ATP, and creatine kinase. Some studies found abnormal TCA cycle metabolites associated with ASD. Thirteen controlled studies reported mitochondrial DNA (mtDNA) deletions or variations in the ASD group in blood, peripheral blood mononuclear cells, lymphocytes, leucocytes, granulocytes, and brain. Meta-analyses discovered significant differences (p < 0.01) in copy number of mtDNA overall and in ND1, ND4 and CytB genes. Four studies linked specific mtDNA haplogroups to ASD. A series of studies found a subgroup of ASD with elevated mitochondrial respiration which was associated with increased sensitivity of the mitochondria to physiological stressors and neurodevelopmental regression. Lactate, pyruvate, lactate-to-pyruvate ratio, carnitine, and acyl-carnitines were associated with clinical features such as delays in language, social interaction, cognition, motor skills, and with repetitive behaviors and gastrointestinal symptoms, although not all studies found an association. Lactate, carnitine, acyl-carnitines, ATP, CoQ10, as well as mtDNA variants, heteroplasmy, haplogroups and copy number were associated with ASD severity. Variability was found across biomarker studies primarily due to differences in collection and processing techniques as well as the intrinsic heterogeneity of the ASD population. Several studies reported alterations in mitochondrial metabolism in mothers of children with ASD and in neonates who develop ASD. Treatments targeting mitochondria, particularly carnitine and ubiquinol, appear beneficial in ASD. The link between mitochondrial dysfunction in ASD and common physiological abnormalities in individuals with ASD including gastrointestinal disorders, oxidative stress, and immune dysfunction is outlined. Several subtypes of mitochondrial dysfunction in ASD are discussed, including one related to neurodevelopmental regression, another related to alterations in microbiome metabolites, and another related to elevations in acyl-carnitines. Mechanisms linking abnormal mitochondrial function with alterations in prenatal brain development and postnatal brain function are outlined. Given the multisystem complexity of some individuals with ASD, this review presents evidence for the mitochondria being central to ASD by contributing to abnormalities in brain development, cognition, and comorbidities such as immune and gastrointestinal dysfunction as well as neurodevelopmental regression. A diagnostic approach to identify mitochondrial dysfunction in ASD is outlined. From this evidence, it is clear that many individuals with ASD have alterations in mitochondrial function which may need to be addressed in order to achieve optimal clinical outcomes. The fact that alterations in mitochondrial metabolism may be found during pregnancy and early in the life of individuals who eventually develop ASD provides promise for early life predictive biomarkers of ASD. Further studies may improve the understanding of the role of the mitochondria in ASD by better defining subgroups and understanding the molecular mechanisms driving some of the unique changes found in mitochondrial function in those with ASD.

Pathogenic/likely pathogenic mutations identified in Vietnamese children diagnosed with autism spectrum disorder using high-resolution SNP genotyping platform

Among the most prevalent neurodevelopmental disorders, Autism Spectrum Disorder (ASD) is highly diverse showing a broad phenotypic spectrum. ASD also couples with a broad range of mutations, both de novo and inherited. In this study, we used a proprietary SNP genotyping chip to analyze the genomic DNA of 250 Vietnamese children diagnosed with ASD. Our Single Nucleotide Polymorphism (SNP) genotyping chip directly targets more than 800 thousand SNPs in the genome. Our primary focus was to identify pathogenic/likely pathogenic mutations that are potentially linked to more severe symptoms of autism. We identified and validated 23 pathogenic/likely pathogenic mutations in this initial study. The data shows that these mutations were detected in several cases spanning multiple biological pathways. Among the confirmed SNPs, mutations were identified in genes previously known to be strongly associated with ASD such as SLCO1B1, ACADSB, TCF4, HCP5, MOCOS, SRD5A2, MCCC2, DCC, and PRKN while several other mutations are known to associate with autistic traits or other neurodevelopmental disorders. Some mutations were found in multiple patients and some patients carried multiple pathogenic/likely pathogenic mutations. These findings contribute to the identification of potential targets for therapeutic solutions in what is considered a genetically heterogeneous neurodevelopmental disorder.

Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism

Toxicity of accumulating substrates is a significant problem in several disorders of valine and isoleucine degradation notably short-chain enoyl-CoA hydratase (ECHS1 or crotonase) deficiency, 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency, propionic acidemia (PA), and methylmalonic aciduria (MMA). Isobutyryl-CoA dehydrogenase (ACAD8) and short/branched-chain acyl-CoA dehydrogenase (SBCAD, ACADSB) function in the valine and isoleucine degradation pathways, respectively. Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences. We investigated whether substrate reduction therapy through inhibition of ACAD8 and SBCAD can limit the accumulation of toxic metabolic intermediates in disorders of valine and isoleucine metabolism. Using analysis of acylcarnitine isomers, we show that 2-methylenecyclopropaneacetic acid (MCPA) inhibited SBCAD, isovaleryl-CoA dehydrogenase, short-chain acyl-CoA dehydrogenase and medium-chain acyl-CoA dehydrogenase, but not ACAD8. MCPA treatment of wild-type and PA HEK-293 cells caused a pronounced decrease in C3-carnitine. Furthermore, deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells. Deletion of ECHS1 in HEK-293 cells caused a defect in lipoylation of the E2 component of the pyruvate dehydrogenase complex, which was not rescued by ACAD8 deletion. MCPA was able to rescue lipoylation in ECHS1 KO cells, but only in cells with prior ACAD8 deletion. SBCAD was not the sole ACAD responsible for this compensation, which indicates substantial promiscuity of ACADs in HEK-293 cells for the isobutyryl-CoA substrate. Substrate promiscuity appeared less prominent for 2-methylbutyryl-CoA at least in HEK-293 cells. We suggest that pharmacological inhibition of SBCAD to treat PA should be investigated further.

Age-associated deficits in social behaviour are microbiota-dependent

Aging is associated with remodelling of immune and central nervous system responses resulting in behavioural impairments including social deficits. Growing evidence suggests that the gut microbiome is also impacted by aging, and we propose that strategies to reshape the aged gut microbiome may ameliorate some age-related effects on host physiology. Thus, we assessed the impact of gut microbiota depletion, using an antibiotic cocktail, on aging and its impact on social behavior and the immune system. Indeed, microbiota depletion in aged mice eliminated the age-dependent deficits in social recognition. We further demonstrate that although age and gut microbiota depletion differently shape the peripheral immune response, aging induces an accumulation of T cells in the choroid plexus, that is partially blunted following microbiota depletion. Moreover, an untargeted metabolomic analysis revealed age-dependent alterations of cecal metabolites that are reshaped by gut microbiota depletion. Together, our results suggest that the aged gut microbiota can be specifically targeted to affect social deficits. These studies propel the need for future investigations of other non-antibiotic microbiota targeted interventions on age-related social deficits both in animal models and humans.

Metabolomics profiling of valproic acid-induced symptoms resembling autism spectrum disorders using 1H NMR spectral analysis in rat model

Prenatal exposure to valproic acid (VPA) has been implicated in the manifestation of autism spectrum disorder (ASD)-like behavioral and functional changes both in human and rodents including mice and rats. The objective of this study was to determine metabolomics profiling and biomarkers related to VPA-induced symptoms resembling ASD using proton nuclear magnetic resonance (1H-NMR) spectral data. VPA was administered to pregnant rats at gestation day 12.5 and effects measured subsequently in male 4-week-old offspring pups. The sociability of VPA-treated animals was significantly diminished and exhibited ASD-like behavior as evidenced by reduction of social adaptation disorder and lack of social interactions. To find biomarkers related to ASD, the following were collected prefrontal brain cortices, urine bladder and blood samples directly from heart puncture. In all samples, principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) displayed significant clustering pattern differences between control and treated groups. Valine, taurine, myo-inositol, 3-hydroxybutyrate and 1,3-dihydroxyacetone were significantly decreased in brain cortices in treated rats. Serum metabolites of glucose, creatine phosphate, lactate, glutamine and threonine were significantly increased in VPA-administered animals. Urinary metabolites of pimelate, 3-hydroxyisovalerate and valerate were significantly reduced in VPA-treated rat, whereas galactose and galactonate levels were elevated. Various metabolites were associated with mitochondrial dysfunction metabolism and central nervous system disorders. Data demonstrated that VPA-induced alterations in endogenous metabolites of serum, urine, and brain cortex which might prove useful as biomarkers for symptoms resembling ASD as a model of this disorder.

Long-term monitoring for short/branched-chain acyl-CoA dehydrogenase deficiency: A single-center 4-year experience and open issues

INTRODUCTION

Short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD) is an inherited disorder of L-isoleucine metabolism due to mutations in the ACADSB gene. The role of current diagnostic biomarkers [i.e., blood 2-methylbutyrylcarnitine (C5) and urine 2-methylbutyrylglycine (2MBG)] in patient monitoring and the effects of proposed treatments remain uncertain as follow-data are lacking. This study presents first systematic longitudinal biochemical assessment in SBCADD patients.

METHODS

A retrospective, observational single-center study was conducted on newborns born between 2017 and 2020 and suspected with SBCADD. Biochemical, molecular, clinical and dietary data collected upon NBS recall and during the subsequent follow-up were recorded.

RESULTS

All enrolled subjects (n = 10) received adequate protein intake and L-carnitine supplementation. Nine subjects were diagnosed with SBCADD. During the follow-up [median: 20.5 (4-40) months] no patient developed symptoms related to SBCADD. No patient normalized serum C5 and urine 2MBG values. In 7/9 SBCADD patients mean serum C5 values decreased or stabilized compared to their first serum C5 value. A major increase in serum C5 values was observed in two patients after L-carnitine discontinuation and during intercurrent illness, respectively. Urine 2MBG values showed moderate intra-patient variability.

DISCUSSION

The relatively stable serum C5 values observed during L-carnitine supplementation together with C5 increase occurring upon L-carnitine discontinuation/intercurrent illness may support the value of serum C5 as a monitoring biomarker and the benefit of this treatment in SBCADD patients. The role of urine 2MBG in patient monitoring remains uncertain. As all patients were asymptomatic, no association between biochemical parameters and clinical phenotype could be investigated in this study.

Effects of l-Carnitine in Patients with Autism Spectrum Disorders: Review of Clinical Studies

Carnitine is an amino acid derivative, which plays several important roles in human physiology, in the central nervous system, and for mitochondrial metabolism, in particular. Altered carnitine metabolic routes have been associated with a subgroup of patients with autism spectrum disorders (ASD) and could add to the pathophysiology associated with these disorders. We review the current evidence about the clinical effects of carnitine administration in ASD in both non-syndromic forms and ASD associated with genetic disorders. Two randomized clinical trials and one open-label prospective trial suggest that carnitine administration could be useful for treating symptoms in non-syndromic ASD. The effect of carnitine administration in ASD associated with genetic disorders is not conclusive because of a lack of clinical trials and objectives in ASD evaluation, but beneficial effects have also been reported for other comorbid disorders, such as intellectual disability and muscular strength. Side effects observed with a dose of 200 mg/kg/day consisted of gastro-intestinal symptoms and a strong, heavy skin odor. Doses of about 50–100 mg/kg/day are generally well tolerated. Further clinical trials with the identification of the subgroup of ASD patients that would benefit from carnitine administration are warranted.

Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening

Short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) is an autosomal recessive disorder of impaired isoleucine catabolism caused by mutations in the ACADSB gene. There are limited SBCADD cases worldwide and to date no Chinese patients with SBCADD have been reported. The aim of this study was to investigate the biochemical, clinical information, and genotypes of twelve patients with SBCADD in China for the first time. The estimated incidence of SBCADD was 1 in 30,379 in Quanzhou, China. The initial newborn screening (NBS) results revealed that all patients showed slightly or moderately elevated C5 concentrations with C5/C2 and C5/C3 ratios in the reference range, which has the highest risk of being missed. All patients who underwent urinary organic acid analysis showed elevation of 2-methylburtyrylglycine in urine. All patients were asymptomatic at diagnosis, and had normal growth and development during follow-up. Eight different variants in the ACADSB gene, including five previously unreported variants were identified, namely c.596A > G (p.Tyr199Cys), c.653T > C (p.Leu218Pro), c.746del (p.Pro249Leufs*15), c.886G > T (p.Gly296*) and c.923G > A (p.Cys308Tyr). The most common variant was c.1165A > G (33.3%), followed by c.275C > G (20.8%). All previously unreported variants may cause structural damage and dysfunction of SBCAD, as predicted by bioinformatics analysis. Thus, our findings indicate that SBCADD may be more frequent in the Chinese population than previously thought and newborn screening, combined with genetic testing is important for timely diagnosis. Although the clinical course of Chinese patients with SBCADD is likely benign, longitudinal follow-up may be helpful to better understand the natural history of SBCADD.

Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature

Background Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency is a rare inborn error of metabolism with uncertain clinical significance. As it leads to C5-carnitine (i.e. isovalerylcarnitine, 2methylbutyrilcarnitine, or pivaloylcarnitine) elevation, SBCAD deficiency is detectable at newborn screening, requiring differential diagnosis from isovaleric acidemia and pivalic acid administration. Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency. Methods We report two cases of SBCAD deficiency and provide a review of the available literature on this condition. Results Two siblings newly diagnosed with SBCAD deficiency are reported. Newborn screening allowed the early diagnosis in the second-born (C5=0.5 μmol/L, normal 0.05-0.3 μmol/L) and addressed selective screening in the 5-year asymptomatic brother (C5=1.9 μmol/L). Both patients showed increased urinary excretion of 2MBG and two mutations in the ACADSB gene (c.443C>T/c.1145C>T). Currently, both the patients are asymptomatic. Longitudinal biochemical monitoring of the two patients while on treatment with carnitine (100 mg/kg/day) was provided. Based on our experience and the literature review (162 patients), SBCAD deficiency is symptomatic in about 10% of reported patients. Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive. On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop. Acute metabolic decompensation due to catabolic stressors can occur, as observed in one newly reported patient. Fifteen mutations in the ACADSB gene are known, including the newly identified variant c.1145C>T (p.Thr382Met), variably associated to the phenotype. In the Hmong population, SBCAD deficiency is highly prevalent, mostly due to the founder mutation c.1165A>G, and is largely asymptomatic. Conclusions Although mostly asymptomatic, considering SBCAD deficiency as a non-disease in non-Hmong subjects appears unsafe. Catabolic situations can precipitate acute metabolic decompensation. Carnitine supplementation and valproate avoidance appear to be indicated. Providing an emergency protocol for the management of acute catabolic episodes seems reasonable in asymptomatic patients with SBCAD deficiency. Longitudinal follow-up is recommended.

Aspects of Newborn Screening in Isovaleric Acidemia

Isovaleric acidemia (IVA), an inborn error of leucine catabolism, is caused by mutations in the isovaleryl-CoA dehydrogenase (IVD) gene, resulting in the accumulation of derivatives of isovaleryl-CoA including isovaleryl (C5)-carnitine, the marker metabolite used for newborn screening (NBS). The inclusion of IVA in NBS programs in many countries has broadened knowledge of the variability of the condition, whereas prior to NBS, two distinct clinical phenotypes were known, an "acute neonatal" and a "chronic intermittent" form. An additional biochemically mild and potentially asymptomatic form of IVA and its association with a common missense mutation, c.932C>T (p.A282V), was discovered in subjects identified through NBS. Deficiency of short/branched chain specific acyl-CoA dehydrogenase (2-methylbutyryl-CoA dehydrogenase), a defect of isoleucine degradation whose clinical significance remains unclear, also results in elevated C5-carnitine, and may therefore be detected by NBS for IVA. Treatment strategies for the long-term management of symptomatic IVA comprise the prevention of catabolism, dietary restriction of natural protein or leucine intake, and supplementation with l-carnitine and/or l-glycine. Recommendations on how to counsel and manage individuals with the mild phenotype detected by NBS are required.

Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin

Short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD), also called 2-methylbutyryl CoA dehydrogenase deficiency (2-MBCDD), is a disorder of l-isoleucine metabolism of uncertain clinical significance. SBCADD is inadvertently detected on expanded newborn screening by elevated 2-methylbutyrylcarnitine (C5), which has the same mass to charge (m/s) on tandem mass spectrometry (MS/MS) as isovalerylcarnitine (C5), an analyte that is elevated in isovaleric acidemia (IVA), a disorder in leucine metabolism. SBCADD cases identified in the Hmong-American population have been found in association with the c.1165 A>G mutation in the ACADSB gene. The purposes of this study were to: (a) estimate the prevalence of SBCADD and carrier frequency of the c.1165 A>G mutation in the Hmong ethnic group; (b) determine whether the c.1165 A>G mutation is common to all Hmong newborns screening positive for SBCADD; and (c) evaluate C5 acylcarnitine cut-off values to detect and distinguish between SBCADD and IVA diagnoses. During the first 10years of expanded newborn screening using MS/MS in Wisconsin (2001-2011), 97 infants had elevated C5 values (≥0.44μmol/L), of whom five were Caucasian infants confirmed to have IVA. Of the remaining 92 confirmed SBCADD cases, 90 were of Hmong descent. Mutation analysis was completed on an anonymous, random sample of newborn screening cards (n=1139) from Hmong infants. Fifteen infants, including nine who had screened positive for SBCADD based on a C5 acylcarnitine concentration ≥0.44μmol/L, were homozygous for the c.1165 A>G mutation. This corresponds to a prevalence in this ethnic group of being homozygous for the mutation of 1.3% (95% confidence interval 0.8-2.2%) and of being heterozygous for the mutation of 21.8% (95% confidence interval 19.4-24.3%), which is consistent with the Hardy-Weinberg equilibrium. Detection of homozygous individuals who were not identified on newborn screening suggests that the C5 screening cut-off would need to be as low as 0.20μmol/L to detect all infants homozygous for the ACADSB c.1165 A>G mutation. However, lowering the screening cut-off to 0.20 would also result in five "false positive" (non-homozygous) screening results in the Hmong population for every c.1165 A>G homozygote detected. Increasing the cut-off to 0.60μmol/L and requiring elevated C5/C2 (acetylcarnitine) and C5/C3 (propionylcarnitine) ratios to flag a screen as abnormal would reduce the number of infants screening positive, but would still result in an estimated 5 infants with SBCADD per year who would require follow-up and additional biochemical testing to distinguish between SBCADD and IVA diagnoses. Further research is needed to determine the clinical outcomes of SBCADD detected on newborn screening and the c.1165 A>G mutation before knowing whether the optimal screening cut-off would minimize true positives or false negatives for SBCADD associated with this mutation.

Autism spectrum disorders: the quest for genetic syndromes

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disabilities with various etiologies, but with a heritability estimate of more than 90%. Although the strong correlation between autism and genetic factors has been long established, the exact genetic background of ASD remains unclear. A number of genetic syndromes manifest ASD at higher than expected frequencies compared to the general population. These syndromes account for more than 10% of all ASD cases and include tuberous sclerosis, fragile X, Down, neurofibromatosis, Angelman, Prader-Willi, Williams, Duchenne, etc. Clinicians are increasingly required to recognize genetic disorders in individuals with ASD, in terms of providing proper care and prognosis to the patient, as well as genetic counseling to the family. Vice versa, it is equally essential to identify ASD in patients with genetic syndromes, in order to ensure correct management and appropriate educational placement. During investigation of genetic syndromes, a number of issues emerge: impact of intellectual disability in ASD diagnoses, identification of autistic subphenotypes and differences from idiopathic autism, validity of assessment tools designed for idiopathic autism, possible mechanisms for the association with ASD, etc. Findings from the study of genetic syndromes are incorporated into the ongoing research on autism etiology and pathogenesis; different syndromes converge upon common biological backgrounds (such as disrupted molecular pathways and brain circuitries), which probably account for their comorbidity with autism. This review paper critically examines the prevalence and characteristics of the main genetic syndromes, as well as the possible mechanisms for their association with ASD.

2-Methylbutyrylglycine induces lipid oxidative damage and decreases the antioxidant defenses in rat brain

Short/branched chain acyl-CoA dehydrogenase (SBCAD) deficiency is an autosomal recessive disorder of isoleucine metabolism biochemically characterized by accumulation of 2-methylbutyrylglycine (2MBG) and 2-methylbutyric acid (2MB). Affected patients present predominantly neurological symptoms, whose pathophysiology is not yet established. In the present study, we investigated the in vitro effects of 2MBG and 2MB on important parameters of oxidative stress in cerebral cortex of young rats and C6 glioma cells. 2MBG increased thiobarbituric acid-reactive species (TBA-RS), indicating an increase of lipid oxidation. 2MBG induced sulfhydryl oxidation in cortical supernatants and decreased glutathione (GSH) in these brain preparations, as well as in C6 cells, indicating a reduction of nonenzymatic brain antioxidant defenses. In contrast, 2MB did not alter any of these parameters and 2MBG and 2MB did not affect carbonyl formation (protein damage). In addition, 2MBG-induced increase of TBA-RS levels and decrease of GSH were prevented by free radical scavengers, implying that reactive species were involved in these effects. Furthermore, the decrease of GSH levels caused by 2MBG was not due to a direct oxidative action since this metabolite did not alter sulfhydryl content from a commercial solution of GSH. Nitric oxide production was not altered by 2MBG and 2MB, suggesting that reactive oxygen species possibly underlie 2MBG effects. Finally, we verified that 2MBG did not induce cell death in C6 cells. The present data show that 2MBG induces lipid oxidative damage and reduces the antioxidant defenses in rat brain. Therefore, it may be postulated that oxidative stress induced by 2MBG is involved, at least in part, in the pathophysiology of the brain damage found in SBCAD deficiency.

Advances and challenges in the treatment of branched-chain amino/keto acid metabolic defects

Disorders of branched-chain amino/keto acid metabolism encompass diverse entities, including maple syrup urine disease (MSUD), the 'classical' organic acidurias isovaleric acidemia (IVA), propionic acidemia (PA), methylmalonic acidemia (MMA) and, among others, rarely described disorders such as 2-methylbutyryl-CoA dehydrogenase deficiency (MBDD) or isobutyryl-CoA dehydrogenase deficiency (IBDD). Our focus in this review is to highlight the biochemical basis underlying recent advances and ongoing challenges of long-term conservative therapy including precursor/protein restriction, replenishment of deficient substrates, and the use of antioxidants and anaplerotic agents which refill the Krebs cycle. Ongoing clinical assessments of affected individuals in conjunction with monitoring of disease-specific biochemical parameters remain essential. It is likely that mass spectrometry-based 'metabolomics' may be a helpful tool in the future for studying complete biochemical profiles and diverse metabolic phenotypes. Prospective studies are needed to test the effectiveness of adjunct therapies such as antioxidants, ornithine-alpha-ketoglutarate (OKG) or creatine in addition to specialized diets and to optimize current therapeutic strategies in affected individuals. With the individual life-time risk and degree of severity being unknown in asymptomatic individuals with MBDD or IBDD, instructions regarding risks for metabolic stress and fasting avoidance along with clinical monitoring are reasonable interventions at the current time. Overall, it is apparent that carefully designed prospective clinical investigations and multicenter cohort-controlled trials are needed in order to leverage that knowledge into significant breakthroughs in treatment strategies and appropriate approaches.

Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening

Short/branched chain acyl-CoA dehydrogenase (SBCAD) deficiency, also known as 2-methylbutyryl-CoA dehydrogenase deficiency, is a recently described autosomal recessive disorder of isoleucine metabolism. Most patients reported thus far have originated from a founder mutation in the Hmong Chinese population. While the first reported patients had severe disease, most of the affected Hmong have remained asymptomatic. In this study, we describe 11 asymptomatic non-Hmong patients brought to medical attention by elevated C5-carnitine found by newborn screening and one discovered because of clinical symptoms. The diagnosis of SBCAD deficiency was determined by metabolite analysis of blood, urine, and fibroblast samples. PCR and bidirectional sequencing were performed on genomic DNA from five of the patients covering the entire SBCAD (ACADSB) gene sequence of 11 exons. Sequence analysis of genomic DNA from each patient identified variations in the SBCAD gene not previously reported. Escherichia coli expression studies revealed that the missense mutations identified lead to inactivation or instability of the mutant SBCAD enzymes. These findings confirm that SBCAD deficiency can be identified through newborn screening by acylcarnitine analysis. Our patients have been well without treatment and call for careful follow-up studies to learn the true clinical impact of this disorder.

Serum levels of 25-hydroxyvitamin D in mothers of Swedish and of Somali origin who have children with and without autism

AIM

To analyse serum levels of 25-hydroxyvitamin D in mothers of Somali origin and those of Swedish origin who have children with and without autism as there is a growing evidence that low vitamin D impacts adversely on brain development.

METHOD

Four groups of mothers were invited to participate; 20 with Somali origin with at least one child with autism, 20 with Somali origin without a child with autism, 20 of Swedish origin with at least one child with autism and 20 with Swedish origin without a child with autism. Two blood samples were collected from each individual; during autumn and spring.

RESULTS

Between 12 and 17 mothers from the different groups accepted to participate, both groups of mothers of Somali origin had significantly lower values of 25-hydroxyvitamin D compared with Swedish mothers. The difference of 25-hydroxyvitamin D between mothers of Somali origin with and without a child with autism was not significant.

CONCLUSION

Our findings of low vitamin D levels in Somali women entail considerable consequences in a public health perspective. The observed tendency, i.e. the lowest values in mothers of Somali origin with a child with autism was in the predicted direction, supporting the need for further research of vitamin D levels in larger samples of Somali mothers of children with and without autism.

Parental consanguinity is associated with a seven-fold increased risk of progressive encephalopathy: a cohort study from Oslo, Norway

BACKGROUND/OBJECTIVE

Progressive encephalopathy (PE) is a heterogeneous group of individually rare diseases, many with an autosomal recessive mode of inheritance. We estimated the increased risk of PE associated with consanguinity.

PATIENTS AND METHODS

Using a historic cohort study design, the exposures were country of origin (Pakistan versus Norway) and consanguinity. We included children living in Oslo, born between 1985 and 2003. PE cases were retrieved from an electronic registry of diagnoses coded according to the International Classification of Diseases. Incidence rates were calculated for country of origin. We also estimated population attributable risks caused by consanguinity.

RESULTS

We identified 30 cases per 79 704 person years with Pakistani origin and 35 cases per 658 932 person years with Norwegian origin. This gave incidence rates of 37.6 and 5.3 per 100 000 person years, whereas the incidence rate ratio was 7.1 (95% CI: 4.2-11.9). The incidence rates of consanguineous versus non-consanguineous of Pakistani origin were 59.6 and 18.7 per 100 000 person years. The incidence rate ratio was 3.2 (95% CI: 1.4-7.2), whereas the incidence rate ratio of non-consanguineous Pakistani versus non-consanguineous Norwegian origin was 3.5 (95% CI: 1.6-7.6). The incidence rate ratio between consanguineous Pakistanis and Norwegians was 11.2. The population attributable risk due to parental consanguinity was 50.3% in the Pakistani sub-population.

CONCLUSIONS

We found a seven-fold increased risk of PE in the general Pakistani population, and an eleven-fold increased risk in consanguineous Pakistanis. Pakistani origin by itself was also an independent risk factor. Avoidance of consanguinity in the Pakistani population would result in at least 50% reduction of PE in that group.

Prevalence of autism in children born to Somali parents living in Sweden: a brief report

In a geographical area of Stockholm, with a relatively large Somali immigrant population, parents as well as teachers in special schools and staff at habilitation centres have raised concerns over whether children with a Somali background are over-represented in the total group of children with autism. The aim of the study was, therefore, to investigate the prevalence of autism in children with parents from Somalia, living in Stockholm county, and to compare the prevalence in children of Somali background with that in the non-Somali group. We reviewed the records of 17 children (13 males, four females), born between 1988 and 1998 (age range 7-17y) and with a Somali background, who had a diagnosis of autistic disorder or pervasive developmental disorder not otherwise specified (PDDNOS) and were registered at either of the two autism habilitation centres for school-aged children. The prevalence of autistic disorder or PDDNOS was found to be three to four times higher than in the non-Somali group (0.7% vs 0.19%). All children also had learning disability.* Our findings warrant further investigations of possible aetiological factors behind the increased prevalence of autistic disorders in children of Somali origin found in this area in Sweden.